To help_seeker12:
I would say sending the 'job offer' letter to you only after receiving an approved/positive LMO is solely at the discretion of the prospective employer. I can understand why your employer would not, as if I was in their shoes, I would not either until I knew for certain I was actually going to even be able to hire you, the temporary foreign worker, in the first place. In addition, depending on whether or not the 'job offer' for your employer includes some sort of 'moving allowance' or not, that would surely be a factor in the decision to hold off on giving you that or not just yet. Personally, if I was in the same boat as your employer, I would not give one out to you until a positive LMO would come in. Of course this probably varies by employer, but I do not see this as abnormal at all.
Finally, as for the timeline of the LMO and the work permit process, as you can see from just this thread/forum alone (it's a great one at that), the timeframe varies so broadly it is hard to determine. I have followed this thread for a little while now, as well as finding a few others for Alberta, and I can fairly say for sure the approximate timeframe of an Alberta LMO to be returned is around 4-12 weeks, as of 27 July 2012. Of course, some get it far later, but I'd like to think the majority will receive theirs in under 12 weeks. It depends on many things, some including the backlog at the office for which the LMO was applied at, the type of job it is, how high of a demand they are for that job, how many Canadians/Permanent Residents applied for it already, the location of the job itself in Alberta, how long and how well was it advertised, if there were any mistakes on the LMO application itself (whether intentional and/or unintentional), how creditable and verifiable the employer is, how quick do they need to fill the position, is the wage and specifics appropriate, and just who you actually get at the Service Canada department that deals with the LMO. I believe that, just in this forum alone, one person got their LMO in about a week, whereas another was still waiting after nearly six months. In all, I think one of the most important parts of it all is just how long the prospective employer is willing to wait for the LMO to actually be able to get you.
Now, that said, the other important piece that is required is the work permit. If you are a visa-exempted person, you could get one at the border if and when a positive LMO gets back to your prospective employer. It would be the quickest way. Otherwise, if you cannot, do so as soon as you can once you have a copy of the positive LMO, as processing times for that alone can be from 1-4 months.
Sadly, this isn't a very easy, or quick, thing to do. Hopefully, it will be worth the wait for you, and your employer. I hope that helps some for you.